This invention relates generally to methods and compositions for inhibiting styrene monomer polymerization.
It is well known that undesirable and costly polymerization is a significant problem during the manufacturing of various vinyl monomers, particularly vinyl aromatic compounds (e.g., styrene, alpha-methylstyrene and vinyl-toluene). Many kinds of polymerization inhibitors have been used in the past to minimize this problem. For instance, inhibitors such as diethylhydroxylamine, phenyl-p-phenylenediamines, tert-butyl catechol, and phenothiazine have been used to control polymer formation.
During the early 1980s, compounds selected from the groups called alkyl-substituted di-nitro-phenols and nitroso-phenols found widespread use in the styrene industry. However, undesired polymerization, especially during monomer purification processes such as distillation, results in loss of the monomer product. Moreover, loss of production due to polymer formation on process equipment continues to cause operating problems for those in the industry. In particular, plugging of distillation column overhead piping and fouling or plugging of condensers has been problematic. Therefore, the industry has sought compositions and methods that are less dangerous to handle, that are effective in multiple phases, and that reduce product losses and production problems.
The present invention provides compositions and methods for inhibiting polymerization of vinyl aromatic monomer. The present inventor has discovered that a composition comprising a bisphenol compound and an oxidized p-phenylenediamine compound may effectively inhibit the undesirable and costly polymerization of vinyl aromatic monomer.